April 11

1875: Samuel Schwabe, who first documented the roughly 10-year sunspot cycle, died. 1900: The U.S. Navy acquired its first submarine. 1908: Masaru Ibuka, who founded the company that became Sony Corporation, was born. 1921: KDKA broadcast the first radio sporting event - a boxing match. 1945: During World War II, American soldiers liberated the Nazi concentration camp of Buchenwald. 1957: A Ryan X-13 Vertijet became the first jet to take-off and land vertically. 1970: Apollo 13 blasted off on a mission to the moon that was disrupted when an explosion crippled the spacecraft; the astronauts managed to return safely. 1984: Challenger astronauts completed the first in-space satellite repair on the Solar Max. 1986: Halley's Comet made its closest approach to Earth this latest appearance. 2001: China Agreed to Release 24 Crewmembers of a U.S. EP-3E Surveillance Plane.